This invention relates generally to antennas and more particularly to a coaxial cavity antenna.
Coaxial antennas have been produced for some time. However, they have all suffered from electrical plane (xe2x80x9cE-planexe2x80x9d) and magnetic plane (xe2x80x9cH-planexe2x80x9d) pattern differences. Specifically, in a typical coaxial radiator, differences in the aperture distributions of the E and H planes cause the E-plane pattern to narrow as frequency increases. This narrowing is not desirable in a dual polarized antenna, that is, the net result is wide azimuth/narrow elevation for one sense of polarization and narrow azimuth/wide elevation for the other sense of polarization. For the case of the dual circularly polarized coaxial antenna, this is undesirable as it results in unacceptable axial ratio performance. Similarly, for a dual linearly polarized coaxial antenna, E and H plane pattern differences result in unacceptable differences in field of view coverage. The differences in the E and H plane patterns also limits the useful operating bandwidth.
Previous coaxial antenna technology has approximately a 30% usable bandwidth. This is achieved by employing various combinations of inner to outer diameter conductors, radial aperture stubs, and miscellaneous other feeding schemes and arrangements.
Accordingly, a need has arisen for a polarization diverse, high gain, wide bandwidth antenna with low dispersion properties. The present invention provides a coaxial cavity antenna that addresses shortcomings of prior systems and methods.
According to one embodiment of the invention, a coaxial cavity antenna includes a generally cylindrical inner conductor sized for propagation of electromagnetic signals in a predetermined frequency range. The coaxial antenna also includes a generally cylindrical outer conductor formed generally coaxial with the inner conductor, and having a larger diameter than the inner conductor. The outer conductor includes an aperture ring disposed at an end of the outer conductor. The outer conductor is positioned with respect to the inner conductor to form a cavity between the inner conductor and the outer conductor. The cavity is sized for propagating electromagnetic signals in a predetermined frequency range. The coaxial cavity antenna also includes a plurality of aperture teeth disposed around the aperture ring, and an iris ring disposed inside the cavity at a predetermined distance from the aperture ring. Furthermore the coaxial cavity antenna includes a plurality of septums coupled to the inner conductor and the iris ring, and a plurality of cable supports coupled to the outer conductor.
The invention provides numerous technical advantages. For example, the problem of a narrow E-plane has been minimized in an antenna in accordance with the present invention. The antennas of the present invention exhibit substantially symmetric E-plane and H-plane performance over reasonably wide angles, such as xc2x160 degrees, and over reasonably wide frequency bandwidths, such as an octave per sub-band. Another advantage of the present invention is that the antennas are scalable, and through the appropriate choice of inner to outer cavity sizes and depths can be nested in a concentric configuration to provide multi-octave performance.
Other advantages offered by the present invention are dual polarization, high gain, relatively small size and weight, wide bandwidth, and excellent amplitude and phase response in terms of pattern control, phase/amplitude tracking, and cross polarization. All of these are over a field of view greater than or equal to xc2x160 degrees. Antennas in accordance with the present invention have been constructed having bandwidths of 0.5 to 2.0 GHz, 2.0 to 8.0 GHz, and even the whole 2.0 to 18.0 GHz range.
Antennas in accordance with the present invention have applications as elements in interferometers, polarimetry antennas, and as various types of reflector feeds. Antennas incorporating the present invention have excellent dispersion properties making them excellent time domain antennas for use in very wideband systems. Antennas in accordance with the present invention can be arrayed in vertical stacks in order to provide increased directivity (gain) by narrowing the elevation beamwidth. In addition, antennas in accordance with the present invention have few mechanical parts, and are relatively simple to machine and assemble, and have proven to be repeatable.
In summary, the present invention provides a novel, wideband, high gain antenna capable of producing dual linear and/or dual circular polarization simultaneously. Desirable symmetric E and H plane patterns over broad bandwidths, heretofore unknown in coaxial antennas, have been achieved through the physical composition of the invention.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.